One of your greatest feats of mass mind control might just be the veil of secrecy around your current stage show, Svengali. Three months in, and almost no one who's seen it has revealed what happens or the centrepiece trick.

That's very lovely of people. I've always asked people to keep it quiet and I'm always delighted that they do.

What are you prepared to tell us about it?

The shows rely on audience participation and they are funny at times and dark and creepy at times. I write it trying to create a rollercoaster for people – what would feel great to experience if you were trapped in a room with me for two hours. The end is tricky because I don't like saying what it's about, so people just have to come along. Sorry, I'm useless at selling my own stuff.

Fortunately you have such devoted fans that you almost don't have to. On your blog you had to ask them not to come to shows with gifts for you…

Yeah, it doesn't work. They either turn up with all manner of edible things, which I'm never quite sure if I should eat, or they make these elaborate presents that I can't take around on tour with us. But you're right, the tours do sell well and I'm a bit spoiled there. I'm sure there will come a day when they don't but now it's nice not having to go around telling people how great what you do is. I'd find that excruciating.

Is there ever a negative response in the crowd?

No, but I get the occasional mad person. There's something about what I do that attracts people who are a little unfinished. I don't get heckled but equally I do have people fainting and shitting themselves, sometimes literally. In a previous show I walked on glass, and you imagine people getting a bit squeamish and having to turn away, but when you hear that someone emptied their bowels in the chair or threw up on the person in front of them, it's quite extreme. In this show I've had someone faint on stage twice – he literally got back up and apologised and then fainted again.

You don't own a TV yourself – does that change your perspective on fame because you wouldn't, for example, know who's huge on The X Factor?

Yes, and the really awful thing is going to awards ceremonies, because I have no idea who anybody is. I get chatting to somebody and they could be a soap star or a runner for a company or a friend of one of those people. There comes a natural point in the conversation where you have to ask what that person does, and it's horrible because if they are very well known they become a bit self-conscious. If I don't ask, it's how rude of me to not ask what they do: "Oh, I met Derren Brown and all he did was talk about himself."

How do you respond when you are not recognised?

I never quite know how to describe what I do. I normally just say, "Oh, I'm a magician", which probably puts fairly naff ideas in people's minds but is pleasantly conversation-stopping.

Do you then have to explain why you won't do a trick for them?

"Er, I haven't got my cards with me" – I usually say something like that. I just make out I'm the worst magician, avoid the subject and make sure they don't turn the conversation back round again.

You are the patron of the National Parrot Sanctuary in Skegness – what is it you particularly like about the birds?

I went to a party when I was a student and they had a mynah bird up in the bedroom where people put their coats. I was completely captivated – I just sat there all night talking to it. The next day I passed a pet shop and they had a conure – it's a little parakeet – in the window. I bought it, not knowing what it was or how to look after it. I said, "What do they eat?" And he said, "Oh, he loves a Twix." So that one didn't last very long.

I got another one, which I had for years, and I made sure I looked after him properly. He died a while back, and then I moved to London and I had a nicer flat and I didn't want birdshit everywhere. I didn't have anything for ages and then just recently I got another one. He's a Blue Quaker called Rasputin, which is a name that somebody suggested on Twitter, and he's a bit rubbish actually. He doesn't seem to say anything. A bad parrot from that point of view, but he's certainly shitting everywhere and doing all the rest of it.

There's a great story that you shaved the two sides of your face with a different razor to test the claims of a new four-bladed razor – is that quite typical of you?

Yes, I did do that for a couple of weeks. At the moment I'm having slightly heated conversations with my make-up artist about moisturiser. Since turning 40 I happily moisturise – I have what's called a regime – but I'm always in two minds because I have no idea if I'm completely wasting my money. They feel nice when they are on but I can't stop wondering, "Am I succumbing to the same nonsense I try to fight against in other areas?" So I have an uneasy relationship with skincare products.

And I notice you have taken to cravats. Is that another symptom of turning 40?

Yes, I've had a slight feeling of wanting to reclaim some of the lifestyle I had in my 20s, which means poncing around in what amounts to pirate clothes. One thing about cravats though is that they make much more sensible gifts on tour because they pack flat. I'm just putting that idea out there.